This invention relates to an apparatus for fluidizing an unbonded particulate bed of the type used to form a foundry mold in casting metal by a lost foam process. More particularly, this invention relates to an apparatus suitable for use with a flask containing an unbonded particulate bed supported upon a gas-permeable partition to force gas through the partition to fluidize the bed, while reducing plugging of the partition by contaminants entrained in the gas.
In a lost foam casting process, a bed of unbonded refractory particles such as loose sand is packed about a polymeric pattern to form a foundry mold. Molten metal poured into the mold decomposes and replaces the pattern to produce a product casting. To embed the delicate pattern, the bed is temporarily fluidized by an intermittent upward forceful gas flow. The pattern is submerged in the fluidized bed and the gas flow is terminated, whereupon the sand compacts about the pattern. The particulate mold may also be fluidized to facilitate removal of the casting.
Accordingly, a typical foundry flask for lost foam casting comprises a box whose interior is divided by a perforated partition into an upper mold compartment containing the particulate bed and a lower plenum. A gas line is connected to the box to introduce gas under pressure into the plenum, whereupon the gas flows through the partition to fluidize the bed. The perforated partition retains the refractory particles of the bed while allowing gas flow therethrough. Dirt or oil entrained in the pressurized gas introduced in the plenum tends to plug the partition, resulting in uneven fluidization. To obtain access to the partition and plenum for cleaning, it is necessary to disassemble the flask, which removes the flask from production for an extended time. In a production operation involving a plurality of flasks, considerable effort may be needed to maintain the many flasks.
Also, in a typical foundry operation, the flask is conveyed among a plurality of work stations and the gas line is intermittently connected to the flask only at those stations where fluidization is required. It is preferred to connect the gas line automatically, as opposed to manually. This is suitably accomplished by a lance inserted into the plenum through an opening in the flask. Sealing members are provided between the lance and the flask. Foundry dirt accumulating on the lance is introduced into the plenum, adding to the problem of partition plugging, and wears the sealing members about the lance, thereby reducing the effectiveness of the seal and necessitating replacement of the sealing members.
Therefore, it is an object of this invention to provide a fluidization apparatus for use with a flask, such as a lost foam foundry flask, containing an unbonded particulate bed supported upon a gas-permeable partition, which apparatus comprises a plenum adapted to automatically combine with the flask at desired times to force gas through the partition to fluidize the bed, but to disengage from the flask at other times, thereby permitting the flask to be conveyed unencumbered to other work stations. The plenum filters dirt, oil or other contaminants entrained in the gas prior to flowing through the partition, thereby reducing plugging of the partition. When disengaged, the plenum is accessible for cleaning and related maintenance. In a production operation involving many flasks, periodic maintenance conveniently performed on the readily accessible plenum, as opposed to the many flasks, reduces overall maintenance for the operation and allows the flasks to remain in production. In addition, gas is fed to the plenum through a line continually connected thereto, thereby avoiding the problems associated with making temporary gas line connections.